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Learning Transition metal complex ions.

I've got my AQA A Level Inorg Chemistry exam in 2 weeks and am really struggling with learning the content for all the complex ions. Could I have some advice on how to learn which reactions are ligand substitution and which are acid/base reaction. I also get so confused with all the colours of the complexes as there are so many similar ones.
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I made a table + used Quizlet (flashcards) to learn all the colours. I've forgotten about the acid/ base reactions + ligand substitutions so I can't help you with that unfortunately :frown:
Original post by callumc_0
I've got my AQA A Level Inorg Chemistry exam in 2 weeks and am really struggling with learning the content for all the complex ions. Could I have some advice on how to learn which reactions are ligand substitution and which are acid/base reaction. I also get so confused with all the colours of the complexes as there are so many similar ones.

Acid-base reactions require there to be an acid and a base.

If you react a metal aqua complex (i.e usually a weak acid) with an aqueous hydroxide (i.e a strong base), then the hydroxide deprotonates the water ligands and this is an acid-base reaction.

If you react a metal aqua complex containing a metal in the +3 oxidation state (i.e a decently strong acid) with a carbonate (i.e a weak base), then you get an acid-base reaction wherein the carbonate deprotonates the water ligands.

So these would be examples of acid-base reactions. Otherwise, you probably have a ligand exchange.

A thought process to follow:

Q1: Does the complex have water ligands?

(If yes, then proceed. If not, then it’s pretty safe to assume it’s a ligand exchange reaction)

Q2: Is it reacting with hydroxide ions?

(If yes, it’s almost certainly an acid-base reaction. If not, then proceed)

Q3: Is it reacting with carbonate ions?

(If yes, then proceed. If not, then it’s pretty safe to assume it’s a ligand exchange reaction)

Q4: Is the metal in the +3 oxidation state (or in a higher oxidation state, such as +4)?

(If yes, then you have an acid-base reaction and the hydroxide will form. If not, it’s a simple precipitation reaction that forms the carbonate).


Edit: the other examples of acid-base reactions you may wish to take note of are when you react a hydroxide or carbonate with an acid. These reactions do not follow the above thought process. You may also with to take note of the handful of reactions where a small amount of ammonia reacts with a transition metal complex to form a hydroxide - this is also acid-base. I kinda forgot about it for a second lol.
(edited 1 month ago)

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